Removing urine from wastewater and using it as fertilizer has the potential to reduce nutrient loads in aquatic environments and promote sustainability through the use of a common waste material.
Excess nitrogen and phosphorus in our waste streams can stimulate algal blooms and create conditions that are hazardous to marine and lake ecosystems and human health. According to the website of the Rich Earth Institute, a Vermont-based company that focuses on using human waste as a resource, most of the nitrogen and phosphorus in wastewater comes from human urine, although it makes up just 1 percent of wastewater. Removing urine could remove 75 percent of the nitrogen and 55 percent of the phosphorus from municipal sewage treatment plants. And these nutrients could then be recycled for use as fertilizer.
The friction is against systems used to the way things are. Sewage infrastructure is being built to get the waste out of the home without much thought, using pre-existing pipes and toilets that people are used to. Urinary diversion would require changing some of these details, while using the diverted material would require greater acceptance of the waste as valuable.
The power of one
Abe Noe-Hays, co-founder of Rich Earth, said the statistics on the place of urine in wastewater got the ball rolling for urine diversion in an attempt to keep it out of the waste stream in the first place.
A urine-diverting toilet takes advantage of the anatomy of the body. When you sit on the toilet, urine naturally goes to the front of the bowl while feces go to the back. Therefore, the front half of a split toilet bowl catches the urine and can direct it to a separate urine-only drain, while the back half remains connected to a wastewater treatment plant as usual. Separate tubes direct the urine to a collection container. This system may not be perfect – good aim is a bonus when used standing and requires some new plumbing – but it does benefit from tweaking the existing infrastructure.
If there is a possibility of mixing with feces, the World Health Organization (believe it or not) has guidelines for how long urine should be stored before using it as fertilizer. After six months at room temperature, the urine has sufficiently self-disinfected to be used on anything, including raw produce, Noe-Hays said.
The key here is that if the urine is just urine, the moment it leaves the body, it’s ready to use as a nitrogen- and phosphorus-rich fertilizer. But a good separation is important. According to Björn Vinnerås, professor of environmental engineering at the Swedish University of Agricultural Sciences, faeces are the main source of pathogens in the collected urine. Urine separation toilets aren’t perfect, he said, and some mixing is inevitable.
If it can be separated, urine can partially sterilize itself. The nitrogen in urine leaves the body as urea, a simple organic compound. Bacteria in pipes typically break down urea into ammonia. When there is urine in a container, the ammonia raises the pH of the solution to around eight or nine. The high pH environment kills any pathogens from the body that may have made their way into the urine, Vinnerås said.
“It’s like a Twinkie,” Noe-Hays said, referring to the long shelf life of urine.
Noe-Hays was part of a study looking at levels of drugs in urine. Caffeine and ibuprofen were among the most common and commonly found. However, after urine was applied to the soil, the drug concentration in the plants was extremely low. According to the study, a person would have to eat a pound of the product every day for about 2,000 years to get the amount of caffeine in a cup of coffee from urine-fertilized products, Noe-Hays said.
Gardeners often use urine as fertilizer, and Noe-Hays said it works wonders from his personal experience. Noe-Hays said there is no necessary nutrient concentration for urine to be used as fertilizer. It depends on the mass of its components. Pour 1,000 gallons of urine on an acre adds about 50 pounds of nitrogen. Using a concentrate 10 times stronger than diluted urine, only 100 gallons would need to be applied to get the same effect, Noe-Hays said. “The hay doesn’t care if you use the concentrate or the dilution,” he continued. “It just depends on how many pounds of fertilizer it’s getting in total.”
In order for urine to be useful as a fertilizer for anything more than a personal garden, it helps to use the ability to concentrate it. A Rich Earth spinoff called Brightwater Tools is working on concentrating urine by freezing it, Noe-Hays said.
Freezing the water from the urine leaves the nutrients in a slurry that can be used on site or shipped to a farm. The concentration of the urine makes the volume more manageable, especially when separation toilets are used in a commercial or office building. Rather than requiring multiple visits from urine-specific trucks to empty the tanks, the concentration hardware allows the urine to be disinfected, pasteurized, and freeze-concentrated on-site. In trials, concentration levels reached a factor of 10, meaning trucks may be coming for collection every few months instead of every week.
Vinnerås mentioned dehydration as another method to make urine fertilizer usable on a larger scale. Part of his research involves stopping urea degradation in pipes. If urea is not broken down, the nitrogen remains solid when dehydrated, resulting in a dry fertilizer containing about 15 to 20 percent nitrogen.
The benefit he sees in producing a dry product is the opportunity to leverage existing chemical fertilizer management infrastructure. Machines for applying dry fertilizer already exist, and storage can be as simple as stacking sacks on top of each other.
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